One of the things that appeals to me about GTD is the matrix of self management which looks at how we maintain control and perspective. Control is achieved through the 5 stages of Mastering Workflow. Perspective is achieved through the Horizons of Focus. This has Runway Next Actions linked to 10000ft Projects which relate to 20000ft Areas of Focus/Responsibility. And so on up to 50000ft. Projects therefore are crucial. They are the glue between your daily activity and where you want to go over the next 12 months or so. In my Weekly Review I focus on my Projects and how they relate to my Areas of Focus - it's like an audit. If there's not a connection I ask myself why. What needs to change? The Runway NAs or the Area of Focus?
I couldn't run my GTD system without Projects.